For the pavement of roadways, walkways, or parking lots, asphalt pavement is used in many cases due to the benefit of easy construction. In the case of roadways, about 95% of roadways are paved by asphalt. Recently, in the asphalt pavement construction, maintenance construction is conducted more often compared to new construction, and hence the amount of asphalt excavated materials or asphalt cut materials produced by the maintenance construction increases. Accordingly, the amount of asphalt recycled aggregate produced in a recycled aggregate factory that receives the asphalt excavated materials or the asphalt cut materials also increases.
Since the recycling of massively produced asphalt recycled aggregate is promoted, recently, the ratio of a recycled hot asphalt mixture using the asphalt recycled aggregate becomes about 75% of a total hot asphalt mixture production amount, and the use ratio (recycle ratio) of the asphalt recycled aggregate occupied in the aggregate of the recycled hot asphalt mixture also increases.
As shown in Pavement Recycling Guide (published by Japan Road Association in November in 2010), since in the production of the recycled hot asphalt mixture, asphalt (old asphalt) degraded and hardened due to a common use is included in the asphalt recycled aggregate, an additive for recycle is generally added to the asphalt recycled aggregate in order to recover the property and the state of the old asphalt. When such an additive for recycle is added, a method of adjusting a mixing amount so that obtained recycled asphalt is mixed at a designed mixing ratio or a method of adjusting a mixing amount so that a compression coefficient of a recycled hot asphalt mixture becomes a target value (a design compression coefficient) is employed.
Further, when the recycled hot asphalt mixture is produced in an actual asphalt mixing plant, the additive for recycle is added generally at the timing of mixing an asphalt recycled aggregate, a new aggregate, and new asphalt by a mixer as shown in Asphalt Mixing Plant Guide (published by Japan Road Association in October in 1996). However, due to the recent trend of the recycling promotion, a recycled hot asphalt mixture in which a use ratio (a recycle ratio) of an asphalt recycled aggregate exceeds 50% is produced more than before. Accordingly, there is a need to increase the additive for recycle addition amount. Consequently, the mixing time needs to be longer than before in order to sufficiently mix and disperse the additive for recycle. When the recycle ratio is high, there is a tendency that the production capacity per unit time is degraded. Alternatively, when a method of extending the additive for recycle mixing time is not selected in order to ensure the production capacity even when the additive for recycle addition amount is increased, a variation in property/state of the obtained mixture increases, and hence a problem arises in that workability and compactibility are degraded during construction.